Fluorosurfactants are typically used as a polymerization aid in the dispersion polymerization of fluoropolymers, the fluorosurfactants functioning as a non-telogenic dispersing agent. For example, an early description of this use of fluorosurfactants is found in U.S. Pat. No. 2,559,752 (Berry). Because of environmental concerns and because fluorosurfactants are expensive, processes have been developed for their recovery from waste water and from aqueous fluoropolymer dispersions.
One method for removal of fluorosurfactants from fluoropolymer dispersions is disclosed in U.S. Pat. No. 4,369,266 and includes the addition of a stabilizing surfactant followed by concentration by ultrafiltration. This patent teaches that a high proportion of the fluorosurfactant can be removed via the aqueous permeate. It is also known to remove fluorosurfactant by adsorption onto an ion exchange resin as taught in U.S. Pat. No. 3,882,153 (Seki et al) and U.S. Pat. No. 4,282,162 (Kuhls). Kuhls teaches recovery of fluorinated emulsifiers dissolved in the aqueous phase after coagulation of the polymer from the dispersion or in aqueous polymer dispersions to be concentrated. US 2003/0125421 A1 (Bladel et al.) also teaches removal of fluorine-containing emulsifiers from fluoropolymer dispersion by contacting with an anion exchanger.
Known processes using anion exchange resins for the removal of fluorosurfactant from fluoropolymer dispersions employ either strongly basic anion exchange resins or weakly basic anion exchange resins. Although weakly basic resins are useful because they can be regenerated more easily, strongly basis resins are preferred when it is desired to reduce fluorosurfactant to very low levels and for high utilization of the resin. Strongly basic ion exchange resins also have the advantage of less sensitivity to the pH of the media.
Strongly basic resins disclosed for use of the removal of fluorosurfactant from dispersion employ a styrene-divinyl benzene polymer matrix with trimethyl amine groups on benzyl groups of the matrix polymer, i.e., providing quaternary ammonium functionality. For example, Bladel et al. teaches to the use of a resin sold by Rohm and Haas under the trademark AMBERLITE® 402 which contains trimethyl amine moieties in the anion exchange groups. Use of anion exchange resins of this type are prone to the release of trimethylamine in very small quantities into the dispersion. This is due to residual trimethyl amine in the resin and the gradual degradation of the ion exchange groups, which degradation is accelerated by higher dispersion treatment temperatures. Trialkyl amines such as trimethylamine, has a strong odor even in minute quantities (odor threshold of 5 ppb) which can be objectionable when the dispersion is processed.